To assembly a product from parts, an enormous number of parts are required. The larger the number of parts becomes, the more enormous and complex the works become.
Conventionally, an experienced chief of the workshop, who knows the enormous number of complex works well manually arranges the works, calculates the manhour, and assigns operators in units of manhours.
However, this manual composing operation accompanies poor maintenance because it is not only time-consuming but also difficult to correct and can be understood only by the creator.